Fuel cells which include bipolar plates and a membrane electrode assembly situated therebetween have seals which are situated in a seal space around an active area of the fuel cell. Tolerances in the x and y directions as well as the dimensions of the compressed seal influence how wide the seal space is defined. The remaining space between the seal space and the compressed seal may define one or multiple bypass paths.
In the event that the seal is situated on the membrane electrode assembly, this bypass path may occupy a not inconsiderable portion. In some cases, as much as forty percent of the gas may flow via this bypass path. This problem may result, for example, in the fact that the stability decreases, a greater sensitivity at low stoichiometric ratios arises, the water management process deteriorates and/or the optimum operating conditions change.
On the bipolar plates in fuel cells, part of the gas, generally hydrogen and air, bypasses the active surface without participating in the reaction. These bypass paths reduce the pressure loss of the flow in the flow field.
DE 11 2005 002 035 T5 proposes a seal configuration, with the aid of which bypass areas are reduced. For this purpose, sub-seals are situated on both sides of a membrane electrode assembly, between the latter and adjacent bipolar plates. An elastomer sealing element, which spreads apart individual layers of the membrane electrode assembly, is provided within the membrane electrode assembly. A cross-sectional surface of the bypass is reduced by this spreading apart.